Stretchable electronics have attracted great interest from both academia and industry. This new class of electronics has potential applications in many areas such as stretchable cyber skins for robotic devices, wearable electronics for functional clothes, stretchable sensors, and flexible electronic displays. Stretchability of materials is especially desired in electronic devices which need to be in contact with human body or to be conformable with curved surfaces. However, conventional electronic devices are usually made from rigid materials and they are not able to be stretched, folded, and twisted.
Silver is of particular interest as a conductive element for electronic devices because silver is much lower in cost than gold and silver possesses much better environmental stability than copper. Solution-processable conductors are of great interest for use in such electronic applications. Silver nanoparticle-based inks represent a promising class of materials for electronics applications. However, most silver (and gold) nanoparticles often require large molecular weight stabilizers to ensure proper solubility and stability in solution. These large molecular weight stabilizers inevitably raise the annealing temperatures of the silver nanoparticles above 200° C. In order to burn off the stabilizers, which temperatures are incompatible with most low-cost plastic substrates such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) that the solution may be coated onto and can cause damage thereto.
U.S. Pat. No. 7,270,694, which is hereby incorporated by reference herein in its entirety, discloses a process comprising reacting a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an optional solvent, to form a plurality of silver-containing nanoparticles with molecules of the stabilizer on the surface of the silver-containing nanoparticles.
U.S. Pat. No. 7,494,608, which is hereby incorporated by reference herein in its entirety, discloses a composition comprising a liquid and a plurality of silver-containing nanoparticles with a stabilizer, wherein the silver-containing nanoparticles are a product of a reaction of a silver compound with a reducing agent comprising a hydrazine compound in the presence of a thermally removable stabilizer in a reaction mixture comprising the silver compound, the reducing agent, the stabilizer, and an organic solvent wherein the hydrazine compound is a hydrocarbyl hydrazine, a hydrocarbyl hydrazine salt, a hydrazide, a carbazate, a sulfonohydrazide, or a mixture thereof, and wherein the stabilizer includes an organoamine.
Silver nanoparticles have also been prepared, for example as described in U.S. Pub. No. 2007/0099357 A1, incorporated by reference herein in its entirety, using 1) amine-stabilized silver nanoparticles and 2) exchanging the amine stabilizer with a carboxylic acid stabilizer.
There is a great need to develop new materials that can overcome limitations of those currently used in rigid, conventional electronic devices.